Instructions
Oscilloscope bandwidth is expensive, don't reduce it further with
a slow probe. Expensive fast scope probes have high input impedance,
which we do not need when looking at digital IC outputs. Oscilloscopes
have more gain than we need for digital signals. So, let's sacrifice
input impedance and voltage sensitivity, and save money.
Take a 3-ft piece of RG174 50-Ohm coax cable with a 50-ohm terminating
BNC connector on one end, attach a 950 ohm (or 1 kilohm) small resistor
to the other end and use a very short ground connection. Keep the
ground-loop shorter than 0.5 inch.
| Rise Time Budget |
|
| Ground loop (half-inch diameter) |
0.17 ns |
| 3-ft coax |
0.05 Ns |
| BNC connector with 50 Ohm termination |
0.01 Ns |
Total rise time of 0.2 Ns means a bandwidth of 2 GHz. Input impedance
1 kilohm, input capacitance < 2 pF, attenuation 20:1.
|
